.white
.black
.saturation
  position absolute
  top 0
  left 0
  right 0
  bottom 0
  
.saturation
  .white 
    background linear-gradient(to right, #fff, rgba(255,255,255,0))
  .black
    background linear-gradient(to top, #000, rgba(0,0,0,0))
  .pointer
    position absolute
  .circle
    cursor head
    width 4px
    height 4px
    box-shadow 0 0 0 1.5px #fff, inset 0 0 1px 1px rgba(0,0,0,.3), 0 0 1px 2px rgba(0,0,0,.4)
    border-radius 50%
    transform translate(-2px, -2px)